I've been obsessed with California condors for some time, possibly because my own local zoo in Los Angeles has been at the forefront of the California Condor Recovery Program. It's one of the coolest examples of science-based conservation in zoos, since baby chicks are often hand-reared by keepers wearing condor puppets. That's to avoid allowing the birds to imprint onto their human caregivers. And faux power poles are sometimes included in their enclosures to train the birds using operant conditioningnot to land on them

The condors wouldn't leave Les Reid alone. In the late 1990s, a pack of them regularly showed up at his house in Pine Mountain Club, California, a small community northwest of Los Angeles. They clambered around on his roof, making a racket. They perched, one by one, on his large patio umbrella, seeming to enjoy the slow slide down its slippery surface and onto the deck below. Once, Reid, a former member of the Sierra Club's board of directors, came home to find that eight young condors had ripped a hole in his screen door and were enthusiastically tearing apart his mattress. When he'd walked in on them, one of the birds had a pair of his underwear dangling from its beak.

Meanwhile, in Los Angeles and San Diego, the scientists and zookeepers who had been responsible for these birds since birth were shaking their heads in frustration. This was not the behaviour they'd hoped for when they began releasing their avian charges into the wild in 1992.

California condors are evolutionary relics of the Pleistocene, when they soared over huge swathes of North America and fed on the carcasses of mastodons and sabre-toothed cats. With 10ft wingspans, spiky neck ruffs that resemble Elizabethan collars, and mottled bald heads that range in colour from bright pink to sickly yellow, they are hardly beautiful. Nonetheless, condors have a certain mystique; in his book Condor (2006), John Nielsen describes the archaic birds as 'the soul of the wilderness'. Although their range has shrunk and their numbers dwindled, condors can still fly up to 100 miles each day in search of food. They read the wind and build their nests in caves carved into cliff faces. They navigate a complex social hierarchy. They do not break into houses and eat underwear.

Angry conservationists accused Reid of corrupting the condors by illegally supplying them with raw meat from the local grocery, a charge he vigorously denied. After all, he'd fought to protect the condor's range back in the 1960s, when he and his wife would often see the vultures on hikes, soaring miles above them. 'That's the way you're supposed to see a condor,' he told Nielsen, decades later. He believed that such wild birds deserved to be left alone, and he knew better than to tempt them toward civilisation.

That hands-off approach to protecting the condor was shared by most mid-century conservationists. But when the total condor population dropped to a mere 22 birds in 1987, scientists decided they needed to take aggressive action to save the species. So they rounded up every last wild condor and brought them to live in the Los Angeles Zoo and the San Diego Zoo Safari Park.

These birds proved prodigious breeders and, a decade later, their children were being regularly released in California and Arizona by scientists working with the condor reintroduction programme. The mischievous birds that began showing up at Reid's house were members of this zoo-bred generation. And it wasn't just the Pine Mountain Club condors that were acting strangely. Around the same time, condors released near the Grand Canyon posed for photographs and swooped past hotel balconies to wild applause from the guests. They lurked along the edges of trails and lunged at passing hikers, ripping off their shoelaces. A field crew in Arizona told The New York Times in 2003 that they'd seen four condors experimenting with what appeared to be group sex. The scientists tasked with keeping the young birds in line (and away from people) compared the job to running a rowdy middle school.

If the captive-breeding programme succeeded in its mission of raising birds that didn't depend on humans for food, shelter, or any other basic necessity of condor life, it failed in other ways. The zoo-bred birds refused to adopt the manners we demand of wild animals. They weren't scared of humans; they weren't even willing to politely ignore us. Rather, they seemed fascinated by us.

Critics of the condor-reintroduction programme – including Reid – were quick to point fingers. The blame, they said, lay with the birds' shoddy parenting. The condor's wild essence had not been passed down to this new generation, and now it was gone forever. For, you see, these birds had never met their biological parents. Instead, they were raised by puppets.

Head on over to Aeon Magazine to read the rest of this excellent essay: Reared by Puppets.